In order to produce a mold for forming a synthetic resin product such as a lamp body or a front lens, the mold is first cut or cast into a predetermined shape, and a molding surface or a parting surface of the mold is then subjected to electric spark machining. Finally, a polishing tool is used to mirror-finish the molding surface or the parting surface. Although a polishing process using a polishing tool may be performed manually, a great deal of skill is required to properly flat-finish a work surface. Moreover, such a polishing process requires time-consuming operations. Therefore, a polishing robot has recently been employed to enhance polishing precision and reduce the time required for the polishing process.
More specifically, a polishing tool is mounted on a spindle at a leading end of an arm of the polishing robot. The polishing tool is set in rotation and pressed against a work surface of the mold and caused to run along the work surface, which is thereby polished.
In order to polish the work surface, a plurality of polishing tools of different grits (roughnesses) ranging from coarse to fine are prepared in advance. After a polishing tool of a certain grit has been used, another polishing tool of a finer grit is mounted on the spindle at the leading end of the arm of the robot. By thus exchanging polishing tools, the polishing operation is performed.
However, according to the aforementioned conventional polishing process, the polishing tool must be manually mounted on and removed from the spindle at the leading end of the arm of the polishing robot. That is, the operation of exchanging polishing tools is performed manually. Therefore, every time polishing tools are exchanged, the polishing process is interrupted. Consequently, it takes a long time to finish the polishing process.
Furthermore, the polishing tool is coupled to the spindle at the leading end portion of the arm of the polishing robot by means of a fastener, specifically, a collet chuck mechanism. In order to exchange polishing tools, the following operations must be performed. First, a wrench is used to loosen the chuck mechanism, and the previously used polishing tool is removed from the leading end portion of the spindle. A new polishing tool is mounted on the spindle, and the chuck mechanism is tightened.
The fact that it takes such a long time to exchange polishing tools also contributes to prolongation of the polishing process. Further, in order to exchange polishing tools, the operator has to stop other ongoing operations temporarily. Another problem is that unless an operator is present at the site where polishing tools are exchanged, the polishing process cannot be carried out. The fact that polishing tools are exchanged manually results in a decrease in the productivity in manufacturing molds.